Photosynthesis

PS Learning Targets 1-9

Photosynthesis Outline

LT’s 1-3: Energy and Old Dead Dudes

LT’s 4 & 5: Light and Structures of PS

LT’s 6-8: Reactions and Factors of PS

ENERGYAll living things need energy to live!– Heterotrophs-get their food by eating other

organisms and turning them into energy (Ex: herbivores, carnivore, decomposers, etc)

– Autotrophs-get their energy by converting light or chemical energy into sugar, and then converting that into energy

(Ex: plants, bacteria, and some protists)

LT 1

ENERGY• The cell will store energy in molecules like

sugars and ATP– Most cells have small stores of ATP that only last

a few seconds, but cannot store energy there long-term.

– Cells will store it long term in carbohydrates/ sugars– Sugar energy > ATP energy 90x greater

ENERGYWhat are the uses for ATP in biochemical

reactions?• Active Transport• Energy to move cell organelles• Making proteins or nucleic acids• PHOTOSYNTHESIS!!!

Understanding PhotosynthesisVan Helmont

**Water and CO2

are needed tomake plants grow**

Do plants grow by taking material out of the soil?• Thought most of it came from the water absorbed•Did not know that the bulk of the mass came from CO2 absorbed from the air.

Priestley

**O2 is made from PS **

Put a flame under a jar and watched it burn out.•Found there was something in the air that caused the flame to burn•Put a mint plant in the jar and found it produced something flames needed.

Ingenhousz

**Plants need light for PS**

•Found that Priestley’s experiment needed light to occur.

LT 2

Photosynthesis Reaction

6 CO2 + 6 H2O light C6H12O6 + 6 O2

From the air

From the roots

From the sun

Made in the dark

rxn

Made in the light

rxn

Will be made into ATP later in

Cellular Respiration

LT 3

Light and Pigments6 CO2 + 6 H2O light C6H12O6 + 6 O2

• Photosynthesis starts with SUNLIGHT!• The light that comes from the sun is WHITE

LIGHT or ROYGBIV (R O Y G B I V)

• The red end is lowerenergy and longer wavelength

• The violet end has higher energy and smaller wavelength

LT 4

Light and Pigments? If plants use visible light, are all

colors/wavelengths/energies equally valuable to PS?

Let’s see…

Read the results of the experiment from Thomas Engelmann in 1803

Light and Pigments• Most plants are GREEN. This means that ROY BIV is absorbed and G is reflected.

• This means that if ROY and BIV are absorbed these are the colors of light that power PS

Pigment – any substance that absorbs light Chlorophyll a – the main pigment in plants that absorbs the sun’s light to power PS

Light and Pigments• There are also other pigments, beside

chlorophyll a, called ACCESSORY PIGMENTS chlorophyll b and carotenoids

• Each pigment has its optimal portion of ROYGBIV for absorption and to fuel PS

• Chlorophyll a is the main pigment for PS, while the accessory pigments help chlorophyll a by expanding the portion of ROYGBIV it can use!

Light and PigmentsChlorophyll a best absorption

occurs around 425nm AND 660nm

Chlorophyll b best absorption occurs around

475nm AND 640nm

Carotenoids best absorption occurs

around 450nm AND 490nm

Therefore, the accessory pigments expand the absorption from about 425nm (V) to 425-490nm (V-B) AND from 660nm (R) to 640-660nm (O-R). More light absorbed = More PSing!!

Cell Structures We Already Know….

Cell Membrane• A phospholipid bilayer embedded with proteins• Selectively permeable • Maintains homeostasis for the cell via – PASSIVE (diffusion, osmosis, or facilitated diffusion)– ACTIVE TRANSPORT (active transport, endocytosis or

exocytosis)

Now…The Leaf and Chloroplasts• The structures plants use for PS

LT 5

The LeafCuticle- the waxy outer covering of a leaf that prevents water loss

Palisdade Layer-layer of long cells where chloroplasts are found and where most of PS occurs

Spongy Mesophyll-random collection of cells with large spaces in between them. Some PS occurs here, but mostly this is where the gases taken in & given off by PS are exchanged between palisade layer and stoma

The Leaf (cont.)

Stoma- openings on the underside of leaves that allow for gas

exchange between the leaf and atmosphere.

Guard Cells-the cells on either side of the stoma that open/close them to let gases in or out OR to keep gases in

The Chloroplast• Organelle responsible for

PHOTOSYNTHESIS!• Disc-like in shape• Green due to the presence of

the pigment Chlorophyll a • Found mostly within the

palisade layer, but some are in the mesophyll too.

• Internal structures include– Thylakoids– StRoma– Granum (sing.) or Grana (pl.)– Lumen

Let’s see this

The Chloroplast (cont.)1 of 2 membranes that surround the

organelle

Fluid between

the thylakoids where the dark rxn occurs

Disc where the pigments of PS are. Where the light rxn

occurs

How Photosynthesis Occurs? So what about the rest of the PS equation; like CO2,

Water, Glucose and O2 ?

6 CO2 + 6 H2O light C6H12O6 + 6 O2

PS occurs in 2 parts1. Light Dependent (or Light Reaction)• This part of the rxn requires LIGHT, H2O, and gives off O2

2. Light Independent (or Dark Reaction)• This part of the rxn requires CO2 and produces the sugar

or glucose

LT’s

6 & 7

Photosynthesis

Reactants

Products

The Light Reaction“I’m So Excited!”

e- e-

electron carriers receive chlorophyll’s electrons the excited e-’s and pass

get very excited from the them along to other sun’s energy molecules. These e-’s

carriers molecules arecalled the ELECTRON TRANSPORT

CHAIN

LT 6

The Light ReactionExamples of a Carrier Molecule:

NADP+

• Takes 2e-’s from chlorophyll and 1H+ from water

NADP+ + 2e- + 1H+ NADPH• Takes energy with it to other cell rxns• Think of it like a UPS truck, picking up “packages” and

dropping them off

ATP

The Light Reaction: Key Concepts• Occurs in the thylakoid membrane of the

chloroplast• Includes Photosystem II and Photosystem I• Needs Light and H2O to start

• Produces O2, NADPH and ATP

Waste!

The Light Reaction: Photosystem II

PS II - In the Thylakoid Membrane (TM)• 1. e- absorb sun’s energy and get highly energized• 2. The proteins in the TM split a water (hydrolysis) to

make H+’s , e-’s , and O2

• 3. e-’s go to ETC (a series of protein carriers)

• 4. Energy from the e-’s pumps H+’s into the TM, changing the [H+] ions (low to high-active transport)

The Light Reaction: Photosystem I

PS I - In the Thylakoid Membrane (TM)• 5. Light is energized again

• 6. e-’s move to the final e- acceptor which adds them to NADP+ to make NADPH

• 7. High [H+] (left over from hydrolysis) diffuse through the enzyme protein ATP synthase to make ATP form ADP (H+ give energy to add a phosphate to ADP)

Let’s See This

The Light Reaction: The Thylakoid Membrane

The Light Reaction: The Thylakoid Membrane

A Little Quiz:1. Put a #1 where there is a higher concentration of H+

2. Draw a squiggly line between PSII and PSI3. Put a #2 on the thylakoid membrane4. Put a #3 in the stroma5. Put a #4 where the e-’s are first energized6. Put a #5 where the e-’s are re-energized7. Put a #6 where hydrolysis occurs8. Put a #7 where active transport is occurring.

The Dark Reaction: Key Concepts

• The second part of PS is called the Dark Reaction,the Calvin Cycle, or the Light Independent Cycle

• It is called the Dark Rxn because this part can take place without light (that is not to say it must be dark,

but if it were, this part could still proceed)

LT 7

The Dark Reaction: Key Concepts• The two products from the Light Reaction, NADPH and

ATP go to the Dark Reaction

• NADPH and ATP have lots of energy in their bonds but they can only hold it for a few minutes

• If the cell wants to hold the energy long-term, they will have to build high energy molecules that can hold it…like GLUCOSE (savings account!)

• This process takes place in the stRoma (outside of thylakoid)

The Dark Reaction

6-ATP

6-NADPH

3 -CO2

3-RuBP’s5 C’s

3-5C RuBP’s

3-6C Compound-Unstable!

6-3C PGA’s

6-3C PGAL’s

5 stay in cycle

1 exits and will become GLUCOSE

From Light Rxn

Calvin Cycle Video

3-ATP

Limiting Factors to PSThere are factors that limit the amount of PS

1. H2O –slow or decrease PS

2. Temperature– Recall that enzymes have particular optimal temperatures– Functions best between 0-35°C– Temperatures above or below these temps slow PS– Very low temps STOP PS

3. Light Intensity- increase intensity = increase PS4. Color of Light – RO and BV preferred

LT 8

Photosynthesis Review• Two rxns: Light and

Dark• Reactants: H2O, CO2,

and Light• Products: O2 and

Glucose• Two Locations: – Light –Thylakoid

Membrane– Dark- StRoma

LT’s

1-8

Photosynthesis Review

1.

2. 8.

3. 4.

5. 6. 7.

9. 10. 11.

12. 13.

Word BankPhotosynthesisATP (2)ThylakoidStromaLight Energy from the sunHigh energy sugarsNADPH (2)OxygenLight-depentdent reactionCalvin CycleChloroplast

Photosynthesis Review

Adaptations for Photosynthesis

• Recall, that normally stomata are OPEN…– during the day, – when light intensity is high, – CO2 levels are low – and/or water levels are high

Sometimes, during the day, the threat of water loss is too great. How do plants adjust for this?

LT’s 9

Some plants do open/close their stomata backwards!

AT NIGHT…• The stomata OPEN and CO2 comes into the plant’s leaves• Instead of RuBP, CO2 is attached to a molecule called PEP and they

become malic acid• Malic acid is stored in the cells’ central vacuoles

DURING THE DAY…• The stomata close. H2O stays in. • Malic acid leaves the central vacuole and is broken down to get CO2

again• The dark reaction then takes place.

Used by plants in very arid (dry) conditions. Called CAM plants